This invention relates to positive displacement hydraulic pumps and, more particularly, to internal/external gear pumps.
Internal/external gear pumps (IX pumps) have an internally toothed gear and an externally toothed gear, which are rotatably mounted in a housing. The externally toothed gear is usually the drive gear, and the internally toothed gear is usually the driven gear. These two gear members have offset rotatable axes and therefore have a single mesh point, which is opposite the maximum offset. When the two gear members are exiting the mesh points, the gear teeth remain engaged for approximately three or four teeth and then separate or are separating during that engagement and create a space between the rotating gear members which is filled with fluid such as hydraulic fluid from a reservoir through a suction port.
The rotation of the gears take the internal/external gears past a crescent or divider which separates the internally toothed member from the externally toothed member and seals flow trapped within the tooth spaces from returning to the inlet port. As the rotation continues, the toothed gear members are directed to come back into mesh, and as the space between the toothed gear members decreases, the fluid found therein is forced to exit through a pressure port. The gear members then, during this fluid exiting procedure, come back into mesh and start about three or four teeth before the full mesh point. There is one full mesh point during the gear rotation. At the full mesh point, the pump body and wear plate form a dam area.
This mesh point, along with the dam area in the body and wear plate, generally forms a boundary between the higher pressure fluid in the discharge port and the low pressure fluid in the intake port. As this mesh point passes across the dam, increasingly more area of the gears is exposed to high pressure building the forces exerted on the gears. The transition of the mesh point into the suction port exhausts the area previously exposed to high pressure, thus generating a force change on the gears which can result in transmission noise that is disturbing to the operator.
Internal/external pumps in the prior art have been known to employ metering grooves for both the inlet port and the discharge port. These metering grooves, however, cannot overlap within the full mesh point without creating excess leakage, which reduces the performance of the pump at its function of fluid transfer. Thus, this noise phenomenon can still occur within IX pumps. In certain environments, noise created by this event can be of concern to the operator. While those skilled in the art know that there is no performance problem, just a slight noise generation, it has still been a desire to eliminate the noise if at all possible.
It is also well known that those skilled in the art find the implementation of noise-reducing grooves difficult to manufacture. These grooves are of a graduated depth, that is, they are very narrow at the outermost point of their depth and they increase in depth as they approach the port with which they intercept. During manufacturing, it is difficult to control the dimensions of the depth and thus they are costly to produce within the pump body.
It is an object of the present invention to provide an improved internal/external gear pump having a noise control recess.
In one aspect of the present invention, the full mesh point of the IX pump is intercepted by a recess, which is communicated with the inlet port of the IX pump.
In another aspect of the present invention, the recess is positioned in a wear plate, which is disposed within a pump housing.
In yet another aspect of the present invention, the wear plate is sufficiently large to encompass the maximum portion of the pump housing covering both the internal/external gears as well as a portion of the outer flange of the housing.
In still another aspect of the present invention, the full mesh point is a dam area, which prevents fluid communication between the pressure port and the suction port.
In yet still another aspect of the present invention, the recess intersects the dam area at a location wherein the fluid communication is only between the dam area and the suction port.
In a further aspect of the present invention, the noise recess has a substantially constant width and depth.